The present invention relates to a device for continuous reeling of a pulp web, particularly a paper web, for example tissue.
The pulp web is carried over a reel drum that is supported at one end on a vertical rocker arm and is then wound onto a winding unit, and the load between the rocker arm and a fixed counterpart is measured by means of a load-sensing device, where the rocker arm can be preloaded against the load-sensing device by means of a preloading element. The pressing force in the nip between the horizontal reel and the reel drum can be measured using this load-sensing device at the rocker arm.
A device of this kind is described in AT 411 590 B (Andritz AG). A load-sensing device determines the pressing force in the nip, located directly between the respective rocker arm and a fixed counterpart in the paper machine frame. Before operations begin, each load-sensing device is preloaded against the respective rocker arm by means of preloading elements. This preloading is necessary because the oscillation and vibrations by the reel drum distort the measuring result. For the purposes of this preload, preloading elements press against the load-sensing devices, thus sustained contact can be guaranteed between the rocker arm and the load-sensing device, and a continuous signal is provided for control purposes. The preloading elements in AT 411 590 B are operated either mechanically (e.g. via springs or spring stacks) or they are operated hydraulically or pneumatically and always tension the rocker arms with a constant load against the respective load-sensing device. After the swivelling levers have been preloaded, the load-sensing devices are calibrated to nip force zero. Then a selected nip force is transferred via the paper roll to the reel drum by the hydraulic cylinders (or pneumatic cylinders) of the primary and secondary arms during operations. This force is measured by the load-sensing devices and the measurement result is used to control the hydraulic cylinders of the primary and secondary arms.
Preloading of the load-sensing device to a constant value before beginning operations has the disadvantage that this preloading weakens in the course of time and as a result of vibrations. Thus, it is not possible to obtain an exact measurement of the nip force. Preloading of the load-sensing device must thus be checked from time to time and re-adjusted; however, this can only be done during a plant shutdown. In addition, the preloading elements are not easily accessible, thus readjustment is very complicated. In addition, preloading of mechanical elements is relatively inaccurate.
A further problem is the changes in the length of the fastening elements for the load-sensing device and preloading elements caused by heat during operation. The tension also changes during operation as a result, leading to fluctuating measurements.